In this lecture, it is a continuation of the SPR Sensors discussed in the last one. We start off with the definition of a Surface Plasmon, which is an oscillation of electrons at the interface between a good conductor and a dielectric. A light is shot at the surface at a specific angle which causes the light to dissipate on the surface of the metal. However, for this light to be able to run parallel to the surface and not be reflected, there has to be an Evanescent Electric Field, which is an electric field confined to a surface. There is a drop off in the magnitude of the light as you move away from the surface in an exponential rate. When the light travels through, it is important to note that there is a refractive index that is effective in the system. There is light traveling between two different material at the same time and that light is going to be dependant on both materials, thus affecting the wave. As the Electromagnetic field travels laterally across, part in the metal and part in dielectric layer, the field "experiences" a refractive index that is the average of the two surfaces. The light that we shoot at the metal must be shot at a particular angle of incidence and polarization. For polarization, the Electric Field component must be perpendicular to the metal surface. We generate the SP Excitation by starting an Electric Field vector going up and down, so some component travels sideways. This leads to the coupling methods, which the most important is the Prism Coupling(Kretschmann Geometry). However, Waveguide Coupling and Grating Coupling Methods do exist. This means that any change in the dielectric permittivity that occurs in the evanescent field region results in a change of SP coupling.
My research group is focused on the application of sub-wavelength optical phenomena and fabrication methods to the development of novel devices and instrumentation for the life sciences. The group is highly interdisciplinary, with expertise in the areas of microfabrication, nanotechnology, computer simulation, instrumentation, molecular biology, and cell biology. In particular, we are working on biosensors based upon photonic crystal concepts that can either be built from low-cost flexible plastic materials, or integrated with semiconductor-based active devices, such as light sources and photodetectors, for high performance integrated detection systems.
Using a combination of micrometer-scale and nanometer-scale fabrication tools, we are devising novel methods and materials for producing electro-optic devices with nanometer-scale features that can be scaled for low-cost manufacturing. Many of our techniques are geared for compatibility with flexible plastic materials, leading to applications such as low cost disposable sensors, wearable sensors, flexible electronics, and flexible displays. Because our structures manipulate light at a scale that is smaller than an optical wavelength, we rely on computer simulation tools such as Rigorous Coupled Wave Analysis (RCWA) and Finite Difference Time Doman (FDTD) to model, design, and understand optical phenomena within photonic crystals and related devices.
In addition to fabricating devices, our group is also focused on the design, prototyping, and testing of biosensor instrumentation for high sensitivity, portability, and resolution. Advanced instruments enable high resolution imaging of biochemical and cellular interactions with the ability to monitor images of biochemical interactions as a function of time. Using the sensors and instrumentation, we are exploring new applications for optical biosensor technology including protein microarrays, biosensor/mass spectrometry systems, and microfluidics-based assays using nanoliter quantities of reagents. The methods and systems developed in the laboratory are applied in the fields of life science research, drug discovery, diagnostic testing, and environmental monitoring. -From Professor Cunningham's Faculty Profile
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University of Illinois at Urbana-Champaign, Urbana, IL